The invention relates to a method of providing a film of a given length on a surface.
The invention also relates to a device for providing a film of a given length on a surface.
The invention further relates to a display screen having a surface and a film provided on this surface by means of such a method.
Such a method, device and display screen are described in, for example, British patent specification GB 2 298 816. This British patent specification discloses a device which is provided with a synthetic material guide rail against which the film to be provided on a display screen of a display tube is held by means of rollers. The device is further provided with a separate pressure roller located next to the guide rail. To provide a film on the display screen, one end of the film is gripped between clamps whereafter the pressure roller, the guide rail and the guide rollers are displaced with respect to the display screen. During displacement of the device, the film moves between the guide rail and the guide rollers towards the display screen where the film is pressed against the display screen by means of the pressure roller.
A drawback of this known method and device is that the provision of the film is relatively complicated.
It is an object of the invention to provide a method by which a film can be provided on a surface in a relatively simple manner.
In the method according to the invention, this object is achieved in that the film is wound around a roller having a circumference which is larger than or equal to the length of the film, whereafter the roller is unwound relative to the surface while the film is transferred from the roller to the surface.
Since the film is transported, transferred and pressed onto the surface by means of the roller, the provision of the film on the surface is relatively simple and insensitive to disturbances.
Moreover, when the film is being provided and pressed onto the surface, forces substantially only transverse to the surface of the film are exerted on the film. As a result, unwanted forces in the plane of the film, which could deform the film, are avoided.
An embodiment of the method according to the invention is characterized in that the film is drawn against the roller by means of vacuum, which vacuum is eliminated proximate to a portion of the film as soon as the portion is located proximate to the surface.
In this way, the whole film can be tightly drawn against the roller so that a good support of the film is guaranteed. Moreover, the side to be provided on the surface remains completely free in this way, so that there will be no contamination due to contact with guide rollers as in the above-mentioned British patent specification.
A further embodiment of the method according to the invention is characterized in that the roller is rotated while the surface is translated relative to the roller, the circumferential speed of the roller being substantially equal to the speed of displacement of the surface.
By rotating the roller and translating the surface relative to the roller, the roller is unwound on the surface in a simple manner.
It is possible to cause the roller to make both a rotating and a translating movement or to move the surface along the stationary roller.
It is a further object of the invention to provide a device with which the drawbacks of the known device are avoided.
In the device according to the invention, this object is achieved in that the device is provided with a roller having a circumference which is larger than or equal to the length of the film to be provided, means for winding a film around the roller and means for unwinding the film relative to the surface.
The film can be supported, transported, transferred and pressed against the surface in a simple manner by means of the roller.
A further object of the invention is to provide a display screen which can be manufactured in an easier manner. The invention is particularly important for flat panel or cylindrical display screens such as are used in display tubes, PDPs (plasma display panels), LCDs (liquid crystal devices) but also for faceplates of display screens.
In the display screen according to the invention, this object is achieved in that the display screen has a surface and a film provided on the surface, which film is provided by means of the method according to the invention.
A film provided on a display screen serves as a protection for the visible part of this display screen. The film thus has a predetermined transmission so that light can exit from the display screen through the film.
In an embodiment of the display screen according to the invention, the transmission of the film proximate to the center of the film is lower than proximate to the edges of the film. In this way, it is possible to increase the transmission in the corners of the film and thus the corners of the display screen with respect to the center.
A further embodiment of the display screen according to the invention is characterized in that the film is provided with at least a dye whose absorption ranges are between emission spectra of phosphors in the display screen. Such a film-integrated dye such as, for example, ZAPON VIOLET 506 of BASF has a positive effect on the light contrast performance of the display screen.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.